In the preferred embodiments, an uninterruptible power supply has multiple UPS modules connected in parallel. Each module has an AC-DC-AC converter and a subcontroller for controlling the operation of the AC-DC-AC converter. A single current sensor senses a total aggregate current flowing from all the modules. Each subcontroller can detect an input voltage, output voltage, and DC bus voltage of each module. Also, each module has unique operating characteristics (e.g., efficiency curve and a responsiveness coefficient K). Operating characteristics data are stored in a memory accessible by the subcontroller. Based on the voltage and current measurements, and the operating characteristics of each module, the subcontrollers perform calculations to determine a DC bus voltage target (unique for each module) that results in each module providing the same output current. Accordingly, only one current sensor is needed, and, consequently, the cost of the UPS device can be reduced.
Legal claims defining the scope of protection, as filed with the USPTO.
1. An uninterruptible power supply (UPS), comprising: a) a plurality of modules connected in parallel, wherein each module includes: 1) an AC-DC-AC converter having a DC bus voltage, 2) a subcontroller for controlling the AC-DC-AC converter; b) a memory readable by the subcontroller, wherein the memory stores a coefficient K that is unique for each module, and wherein the memory stores an efficiency lookup table that is unique for each module; c) a voltage measurement device or devices for measuring in each module: a DC bus voltage; an output voltage, and an input voltage; d) an output current sensor for measuring a total aggregate output current from all the modules; e) instructions stored in the memory for instructing the subcontroller to perform the following steps: 1) for each module, calculating an input current reference from a DC bus voltage target and the measured DC bus voltage; 2) for each module, calculating an input current estimate from the coefficient K and the input current reference; 3) for each module, calculating an output current estimate from the input current estimate, an efficiency value from the lookup table, a measured input voltage and a measured output voltage; 4) for each module, calculating a new DC bus voltage target from the output current estimate and an output current target, 5) for each module, adjusting the AC-DC-AC converter using input current reference so that the DC bus voltage changes towards the new DC bus voltage target.
2. The uninterruptible power supply (UPS) of claim 1 , wherein each module is nominally identical.
3. The uninterruptible power supply (UPS) of claim 2 , wherein the output current target is equal to 1 N ( Total Aggregate Output Current ) , where N is the number of modules.
4. The uninterruptible power supply (UPS) of claim 3 , further comprising a main controller receiving a total aggregate output current measurement from the output current sensor, wherein the main controller is in communication with each subcontroller, and wherein the main controller calculates the output current target and provides the output current target to each subcontroller.
5. The uninterruptible power supply (UPS) of claim 1 , further comprising a main controller receiving a total aggregate output current measurement from the output current sensor wherein the main controller is in communication with each subcontroller.
6. The uninterruptible power supply (UPS) of claim 1 , wherein each module includes a computer-readable memory in communication with a corresponding subcontroller.
7. The uninterruptible power supply (UPS) of claim 1 , wherein the efficiency lookup table provides efficiency values as a function of output current.
8. The uninterruptible power supply (UPS) of claim 1 , wherein the computer-readable memory further including instructions for repeating steps 1-5 at timed intervals.
9. The uninterruptible power supply (UPS) of claim 1 , wherein the DC bus voltage in each module is changed by adjusting an input current reference signal provided to each module.
10. The uninterruptible power supply (UPS) of claim 1 , wherein the input current reference calculation is in the form: Input Current Reference = A ∫ T ( BV target - BV ) ⅆ T + B ( BV target - BV ) where A and B are integral and proportional gain constants.
11. The uninterruptible power supply (UPS) of claim 1 wherein the DC bus voltage target calculation is in the form: DC Bus Voltage Target = BV target = C ∫ T ( I target - I out ) ⅆ T + D ( I target - I out ) where C and D are integral and proportional gain constants.
12. An uninterruptible power supply (UPS), comprising: a) a plurality of nominally identical modules connected in parallel, wherein each module includes: 1) an AC-DC-AC converter having a DC bus voltage, 2) a subcontroller for controlling the AC-DC-AC converter; b) a memory readable by the subcontroller, wherein the memory stores a coefficient K that is unique for each module, and wherein the memory stores an efficiency lookup table that is unique for each module; c) a voltage measurement device or devices for measuring in each module: a DC bus voltage, an AC output voltage, and an AC input voltage; d) an output current sensor for measuring a total aggregate output current from all the modules, wherein an output current target for each module is determined from the total aggregate output current; and e) instructions stored in the memory for instructing the subcontroller to calculate a DC bus voltage target for each module, wherein the DC bus voltage target is calculated from the measured DC bus voltage, a prior DC bus voltage target, the coefficient K, an efficiency value from the lookup table, the AC output voltage, the AC input voltage, and the output current target; wherein the DC bus voltage target is selected such that when each module has a DC bus voltage equal to its DC bus voltage target, each module provides an approximately equal amount of output current.
13. The uninterruptible power supply (UPS) of claim 11 , wherein the instructions in element (e) include instructions for performing the following steps: 1) for each module, calculating an input current reference from the DC bus voltage target and the measured DC bus voltage; 2) for each module, calculating an input current estimate from the coefficient K and the input current reference; 3) for each module, calculating an output current estimate from the input current estimate, an efficiency value from the lookup table, a measured input voltage and a measured output voltage; 4) for each module, calculating a DC bus voltage target from the output current estimate and an output current target. 5) for each module, adjusting the AC-DC-AC converter using input current reference so that the DC bus voltage changes towards the DC bus voltage target; 6) repeating steps 1-5 a plurality of times.
14. A method for calculating a new DC bus voltage target for each module in a multimodule UPS device, wherein each module has a unique coefficient K, and a unique efficiency lookup table, wherein the efficiency lookup table provides efficiency values for a range of output currents, the method comprising the steps of: 1) measuring an input voltage, and output voltage, and a DC bus voltage for each module; 2) for each module, calculating the input current reference from a prior DC bus voltage target and the measured DC bus voltage; 3) for each module, calculating an input current estimate from the coefficient K and the input current reference; 4) for each module, calculating an output current estimate from the input current estimate, an efficiency value from the lookup table, and a measured input voltage and a measured output voltage, and 5) for each module, calculating the new DC bus voltage target from the output current estimate and an output current target.
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
February 19, 2007
February 17, 2009
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